That behaviour is specifically for for (@array). for (@array) is different than other forms of for (LIST). As soon as one iterates over anything but just an array, it's the size of the list on the stack that matters.

The real difference is that for (@array) is optimized to avoid flattening @array onto the stack. Instead, for (@array) navigates @array in place. For all other expressions, a list is formed on the stack and for iterates over that.

The following show the difference between iterating in place, and iterating over a list on the stack.